Speaker
Description
NA62 is the last generation kaon experiment at the CERN SPS aiming to study the ultra-rare $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ decay. According to the Standard Model (SM) prediction, the decay branching ratio (BR) is of O($10^{-10}$) with very small uncertainty. The main goal of the NA62 experiment is the measurement of this BR with 10% accuracy. This is achieved by collecting about 100 $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ events assuming a 10% signal acceptance.
The challenging aspect of NA62 is the suppression of background decay channels with BR up to 10 orders of magnitude higher than the signal and with similar experimental signature, such as $K^+ \rightarrow \mu^+ \nu$. To this purpose, the NA62 experimental strategy requires, among other conditions, good particle identification (PID) capability and rejection power of the kinematic selection.
A key element of PID in NA62 is the Ring-Imaging Cherenkov (RICH) detector, exploiting neon gas at atmospheric pressure as radiator medium. According to the NA62 requirements, the RICH identifies $\mu^+$ and $\pi^+$ in the momentum range between 15 and 35 GeV/c with a muon rejection factor of $10^{-2}$, leaving a muon contamination of about 1% in the pion sample. It also measures the arrival time of charged particles with a precision better than 100 ps, needed to correctly associate the $\pi^+$ with the parent $K^+$ at a kaon decay rate of about 5 MHz, and is one of the main components of the NA62 trigger system.
NA62 has recently presented the result of the 2016 data analysis: one clear $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ event has been detected, compatible with the SM within the errors. The 2017 data analysis is in progress and a long data taking period is in program in 2018, which will greatly improve the present result. The RICH detector has been successfully operated during the 2016 and 2017 data taking periods and it is ready to be exploited in the 2018 run. The main design aspects and operational characteristics of the detector will be described in detail and the general performance, measured with the data collected in the last NA62 running periods, will be summarized.
